References: bsc#962360 CVE-2015-7512

Backends could provide a packet whose length is greater than buffer
size. Check for this and truncate the packet to avoid rx buffer
overflow in this case.

Cc: Prasad J Pandit <address@hidden>
Cc: address@hidden
Signed-off-by: Jason Wang <address@hidden>
---
 hw/net/pcnet.c | 6 ++++++
 1 file changed, 6 insertions(+)

Index: xen-4.6.0-testing/tools/qemu-xen-dir-remote/hw/net/pcnet.c
===================================================================
--- xen-4.6.0-testing.orig/tools/qemu-xen-dir-remote/hw/net/pcnet.c
+++ xen-4.6.0-testing/tools/qemu-xen-dir-remote/hw/net/pcnet.c
@@ -1086,6 +1086,12 @@ ssize_t pcnet_receive(NetClientState *nc
             int pktcount = 0;
 
             if (!s->looptest) {
+                if (size > 4092) {
+#ifdef PCNET_DEBUG_RMD
+                    fprintf(stderr, "pcnet: truncates rx packet.\n");
+#endif
+                    size = 4092;
+                }
                 memcpy(src, buf, size);
                 /* no need to compute the CRC */
                 src[size] = 0;